Tynan is educated at St. Catherine’s, a convent school in Drogheda. Her poetry is first published in 1878. She meets and becomes friendly with the poet Gerard Manley Hopkins in 1886. She goes on to play a major part in Dublin literary circles. In 1898 she marries English writer and barrister Henry Albert Hinkson and they move to England. After her marriage she usually writes under the name Katharine Tynan Hinkson, or variations thereof. Later she lives at Claremorris, County Mayo, when her husband is a magistrate from 1914 until 1919. Of their three children, Pamela Hinkson (1900–1982) was also known as a writer.
For a while, Tynan is a close associate of William Butler Yeats (who may have proposed marriage and been rejected, around 1885), and later a correspondent of Francis Ledwidge. Involved in the Irish Literary Revival, Tynan expresses concern for feminist causes, the poor, and the effects of World War I in her work. She also meditates on her Catholic faith. A prolific writer, she wrote more than one hundred novels, twelve collections of short stories, reminiscences, plays, and more than a dozen books of poetry.
Katharine Tynan Hinkson dies on April 2, 1931 in Wimbledon, London, at the age of 72.